Castering wheels are used on many types of turf maintenance and harvesting equipment. Although the present invention could be used in conjunction with turf maintenance machines and harvesters of any type, for the sake of brevity the invention will be described in terms of a turf mowing machine having one or more rotary cutting units or decks. In a preferred embodiment, the present invention can be used most advantageously as a component of riding rotary mowers. In order to better understand the somewhat unique demands that are placed on castering wheels used on mowing equipment, a brief discussion of rotary mower structures and geometry is necessary.
Larger rotary riding mowers typically include a traction vehicle supported by a plurality of wheels; a prime mover connected through a transmission to one or more of the wheels; one or more rotary decks having mechanically or hydraulically driven blades; and one or more lift arms (or analogous structures) pivotally connected to the traction vehicle suitable for supporting the deck(s). Lift arms are so termed because they lift the decks from their normal operating positions to their transport positions. An example of a rotary mower of this type is disclosed in U.S. Pat. No. 4,854,112, issued to Holley, et al, and which is illustrated generally in FIG. 6 herein.
The mower 10 includes a traction vehicle 12 supported by a pair of front drive wheels 14 and a pair of rear steerable wheels 16. Traction vehicle 12 also carries a prime mover connected through a transmission to drive wheels 14. Traction vehicle 12 supports a front deck 18 and a pair of wing decks 20a and 20b, the blades of which are driven either hydraulically or through a power take-off (PTO) to the prime mover. The decks 18, 20 are shown in their cutting positions in solid line; and in their transport positions in phantom line.
Referring to FIG. 6, the preferred characteristics or features of a rotary deck or cutting unit support system can be appreciated. In the cutting position, the cutting units 20a and 20b are preferably "floated" relative to the traction vehicle 12. That is, the cutting units 20a and 20b are preferably independently and separately supported by the traction vehicle 12 so that they can follow the contours or undulations of the ground regardless of the gross motion of the traction vehicle 12. If cutting units 20a and 20b are not supported in a floating manner, they tend to scalp the higher regions and miss the lower regions. While non floating cutting units might be acceptable for residential use, certainly golf course and estate maintenance require that the cutting units individually follow the subtle variations of the ground to maintain a consistently good cut across the entire swath, regardless of the immediate topography encountered by each individual cutting unit.
The connection between the cutting units and the traction vehicle must also permit lifting of the cutting units from their lowered cutting positions to a raised "transport" position (shown in phantom in FIG. 6). This "transport" position permits the operator to temporarily raise one or more of the cutting units 20a and 20b in order to mow a narrower swath or to pass through a gate or between trees. Also, it is occasionally necessary to drive mowing machines over conventional road surfaces, at which time it is important to raise the cutting units 18, 20a and 20b to a transport position since they are not entirely suitable for repeatedly running up and down over curbs, nor for travel over paved streets at anything approaching the speed of ordinary traffic. In view of this, most riding mowers, such as the one illustrated in FIG. 6, include mechanisms which can raise the cutting units upward and toward the traction vehicle. Although the castering wheels on both decks 18 and 20 are subject to unique operating conditions, the wing decks 20a and 20b consistently place the greatest demands on the castering wheels. The following discussion of deck 20 is, however, also generally applicable to front deck 18. The deck 20 can "float" relative to traction vehicle 12. The struts 40 which support deck 20 are rollably supported at either end by casters 42, the casters 42 serving as ground following devices establishing the height of cut of deck 20. That is, as casters 42 follow ground undulations, struts 40 and housing 24 also "pitch", "roll", "yaw" and translate vertically depending on the terrain. In the mowers heretofore known, the casters 42 are typically free to rotate a full 360 degrees about their support shaft (i.e., vertical) axis.
In the cutting mode, the free rotation of the casters presents several problems. First, the casters should follow (i.e., roll) in the direction of the traction unit. However, due to turning movements of the traction unit or uneven terrain, one or more caster wheels may become substantially misaligned or "cocked" with respect to the drive wheels 14, as may be clearly seen in FIG. 6. When the caster wheel returns to ground contact in such a misaligned state, an instantaneous scraping or scuffing of the turf occurs. Such scuffing is unacceptable in many settings, such as on a golf course. Also, as can be seen by viewing the raised position of deck 20b, the caster wheels 112 and 113 tend to become perpendicularly aligned to their normal ground track due to minute imbalances in each individual caster. When the deck is lowered, the casters initially remain substantially perpendicular to the desired direction of travel. Since the raising and lowering of the deck typically occurs while the mower is in motion (e.g., 12 mph), significant, repeated scuffing can occur. Further, the shock can sometimes be great enough to pull the caster wheel tire from the wheel rim or at least damage the tire.
Other problems with a conventional, freely rotating caster wheel can also occur. If the deck is raised only slightly (for example, to less than a 45 degree angle with respect to a horizontal plane), the minute imbalance of each caster causes the caster to rotate about its support shaft axis, often continuously, thereby becoming a disturbing source of noise. Also, some decks are supported by four separate castering wheels, since the typical terrain is not perfectly flat, one caster wheel is usually suspended above the ground. The "uneven" wheel tends to rotate about its support shaft, creating noise and the potential for scuffing. As can be seen in FIG. 6, the particular geometry of some mowers causes the clearance between drive wheel 14 and caster wheel 42 to be quite small. This is because the designers want the casters to be as close as possible to the cutting blades to enhance ground following. In these situations, caster wheel 42 can actually collide with drive wheel 14, causing caster wheel 42 to momentarily stop rolling along the ground, creating further scuffing of the turf.
Further, the conventional caster support shaft resides within its supporting collar with only lubricant separating the two metal surfaces. Such an arrangement permits lateral loads and vibration affecting the caster wheel to be transmitted directly to the deck itself without any intervening shock absorption. Thus, the castering wheel promotes early deterioration of the deck frame due to twisting and vibration induced stress relief cracks.
As mentioned earlier, the caster wheels serve as the primary means of establishing the height of cut of the rotary blades. In FIG. 6, no particular caster wheel height adjustment mechanism is depicted. Referring to FIG. 2, however, one can view a conventional height adjustment scheme. As seen at castering wheel 4, a fork 5 is rigidly affixed to a shaft 6 which passes through sleeve 7. A series of spacers or "c" rings 50, 51, 52, 53, 54 and 55 is stacked above sleeve 7, the uppermost spacer 50 abutting cotter pin 56. In order to make height adjustments, spacers are removed as needed from above sleeve 7 and placed below sleeve 7 in the region 57. In this way, sleeve 7 is raised above fork 5, thereby incrementally raising deck 58 above surface 59.
In practice, this arrangement presents several disadvantages, insofar as the overall height of the spacer stack (plus the height of sleeve 7 ) does not perfectly match the distance between the upper surface 60 of fork 5 and the cotter pin 56. The stack of spacers is therefore free to rattle. When castering wheel 4 is in motion, this imperfect fit can contribute to shimmying of wheel 4. Such a washer arrangement does virtually nothing to frictionally resist 360 degree rotation of wheel 4 about the axis defined by shaft 6 when deck 58 is raised for transport, and performs a shock transferring, rather than a shock absorbing, function.
Efforts to prevent caster wheel shimmy have been attempted in the past, as is most notably exemplified in U.S. Pat. No. 2,761,692, issued to Sisulak. The Sisulak device requires the use of three springs and a casting containing three parallel bores in order to urge continuous contact between a castering wheel and the ground over which it travels (see Sisulak at column 1, lines 47-54; column 3, lines 37-2). The complexity of the Sisulak device tends to negate the inherent advantage of the castering wheel, namely, its low cost and ease of manufacture. In most cases, it is preferable to permit 360 degree (or some substantial amount) castering in order to accommodate sharp turns of the mower; however, because of space limitations this may not always be possible. Thus a need exists to preserve some of the advantages of a castering wheel of relatively simple design while providing some degree of shock absorption to the mower deck, some restraint on uncontrolled rotation of the castering wheel about its supporting shaft, both when in and out of contact with the ground, and finally to provide some resistance to shimmying and vibration, all while permitting the castering wheel to serve as a convenient means of adjusting the height of cut in a turf maintenance device.